Transparent YAG ceramics by surface softening of nanoparticles in spark plasma sintering

Rapid heating of 34 nm yttrium aluminum garnet (YAG) nanoparticle compacts using pulsed high direct electric current, during the spark plasma sintering (SPS), resulted in transparent ceramics, after 3 min at 100 MPa and 1400 °C. This phenomenon is in contrast to conventional sintering at much higher temperatures that result in translucent or opaque ceramics. Grain growth analysis and the evolved microstructure during the SPS showed that the YAG nanoparticle surfaces soften due to the pulsed direct electric current. Dynamic densification to transparency occurs by nano-grain rotation and sliding, aided by the viscous layer, and followed by curvature driven grain boundary diffusional processes at higher densities and grain sizes.